Handle SLA timers during process instance migration

[martinweiler]

After migrating a process instance, which has an active human task with a defined SLA Due Date, the SLA Compliance remains as "Pending" when the time expires.

To reproduce the problem, create a process model with a human task, put a value in the "SLA Due Date" field, save as V1. Edit the process model and save it as V2. Instantiate a process with V1, then migrate it from V1-->V2, the SLA Compliance does not change when the time expires.

Note: While this description is targeting human tasks, we should make sure that any SLA timers are handled correctly during the migration:

• Process SLA
• Node Instance SLA (including HT)

[elguardian]

PR: kiegroup/jbpm#2323

[martinweiler]

Note that RH also opened JIRAs (including a PR) to address this:

• https://issues.redhat.com/browse/RHPAM-4773
• https://issues.redhat.com/browse/JBPM-10192
• [JBPM-10192] Tests for SLA timers are not migrated after migrating process instances kiegroup/jbpm#2326